error-handling

Error Handling Patterns

Overview

Backend error handling patterns for building robust and debuggable services.

Error Types

Custom Error Classes

// Base application error
class AppError extends Error {
  constructor(
    message: string,
    public code: string,
    public statusCode: number = 500,
    public isOperational: boolean = true
  ) {
    super(message);
    this.name = this.constructor.name;
    Error.captureStackTrace(this, this.constructor);
  }
}

// Specific error types
class ValidationError extends AppError {
  constructor(message: string, public fields?: Record<string, string>) {
    super(message, 'VALIDATION_ERROR', 400);
  }
}

class NotFoundError extends AppError {
  constructor(resource: string, id?: string) {
    super(
      id ? `${resource} with id ${id} not found` : `${resource} not found`,
      'NOT_FOUND',
      404
    );
  }
}

class UnauthorizedError extends AppError {
  constructor(message: string = 'Unauthorized') {
    super(message, 'UNAUTHORIZED', 401);
  }
}

class ForbiddenError extends AppError {
  constructor(message: string = 'Forbidden') {
    super(message, 'FORBIDDEN', 403);
  }
}

class ConflictError extends AppError {
  constructor(message: string) {
    super(message, 'CONFLICT', 409);
  }
}

class RateLimitError extends AppError {
  constructor(public retryAfter: number) {
    super('Too many requests', 'RATE_LIMIT', 429);
  }
}

Error Response Format

Standard Format

interface ErrorResponse {
  error: {
    code: string;
    message: string;
    details?: unknown;
    stack?: string;  // Only in development
  };
  meta: {
    requestId: string;
    timestamp: string;
  };
}

function formatError(error: AppError, requestId: string): ErrorResponse {
  const response: ErrorResponse = {
    error: {
      code: error.code,
      message: error.message,
    },
    meta: {
      requestId,
      timestamp: new Date().toISOString(),
    },
  };

  if (error instanceof ValidationError && error.fields) {
    response.error.details = error.fields;
  }

  if (process.env.NODE_ENV === 'development') {
    response.error.stack = error.stack;
  }

  return response;
}